Fuel injection control apparatus for internal combustion engine

ABSTRACT

In controlling power supply time, a variation in the fuel injection quantity caused by a variation in the fuel injection rate at the in-cylinder pressure of the engine (detected or estimated value in the running state of the internal combustion engine) relative to the fuel injection rate at a reference in-cylinder pressure (under the condition of an injector characteristic measuring benchmark test), and in addition, a variation in the fuel injection start time is corrected. In the calculation of the variation in the fuel injection quantity, a fuel injection rate changing behavior model in which changing behavior of the fuel injection rate is modeled as a trapezoid is used to calculate the areas of Δq 1  and Δq 2 . The variation in the fuel injection start time Δτd is calculated based on the rail pressure and the variation in the in-cylinder pressure. In this way, there is provided a technology for controlling the fuel injection quantity that changes with a change in the in-cylinder pressure with improved accuracy.

TECHNICAL FIELD

The present invention relates to a fuel injection control apparatus foran internal combustion engine.

BACKGROUND ARTS

Conventionally, among direct injection internal combustion engineshaving a fuel injection valve (or an injector) for injecting fueldirectly into the interior of the cylinder, one having a function ofcorrecting the opening time of the fuel injection valve based on thepressure in the interior of the cylinder (or the in-cylinder pressure)is known (see, for example, patent document 1 listed later).

The reason why this function is adopted is that the pressure in theinterior of the cylinder (the in-cylinder pressure) acts as a backpressure against the fuel injection valve. In this function, thein-cylinder pressure that changes in accordance with the runningcondition of the engine is calculated to correct the opening time of thefuel injection valve, thereby obtaining a desired fuel injectionquantity.

However, in the above-described conventional art, the in-cylinderpressure is calculated, and then the fuel injection rate (i.e. thequantity of the fuel injected per unit time) is calculated based on thepressure difference between that in-cylinder pressure and the pressureof the fuel introduced to the fuel injection valve. Then, the openingtime of the fuel injection valve is calculated based on the calculatedfuel injection rate and the required fuel quantity. Thus, in theconventional art as such, no consideration has been given to changes inthe start time of the fuel injection.

This point will be discussed in the following with reference to FIG. 14.FIG. 14 shows changing behavior of the fuel injection rate. In FIG. 14,the vertical axis represents the fuel injection rate, and the horizontalaxis represents the time. In FIG. 14, waveform X and waveform Y of thefuel injection rate show changing behavior of the fuel injection ratefor different in-cylinder pressures but the same rail pressure (i.e. thepressure of the fuel supplied to the fuel injection valve). Fuelinjection rate waveform X represents the case in which the in-cylinderpressure is a reference in-cylinder pressure serving as a reference (forexample, the pressure under the condition in an injector characteristicsmeasuring benchmark test (e.g. 1 Mpa)), and fuel injection rate waveformY represents the case with the engine in-cylinder pressure in theinternal combustion engine in a running state (e.g. 8 Mpa).

As will be seen from FIG. 14, when the in-cylinder pressure increases,the start time of the fuel injection becomes earlier. If the start timeof the fuel injection becomes earlier, the fuel injection quantity willincrease.

FIG. 15 is a fuel injection rate changing behavior model serving as amodel for the changing behavior of the fuel injection rate shown in FIG.14. The inventors of the present invention modeled the changing behaviorof the fuel injection rate shown in FIG. 14 as a trapezoid shown in FIG.15. In FIG. 15, trapezoid X shown by a solid line is a model for fuelinjection rate waveform X in FIG. 14, and trapezoid Y shown by a brokenline is a model for fuel injection rate waveform Y in FIG. 14.

In FIG. 15, letting Q be the area of trapezoid X or the required fuelinjection quantity, Qr be the area of trapezoid Y or the actualinjection quantity, dQ1 be the variation in the fuel injection quantitydue to the variation in the fuel injection rate between in the case ofreference in-cylinder pressure and in the case of in-cylinder pressureof the engine (i.e. the area within trapezoid X above trapezoid Y inFIG. 15), and dQ2 be the variation in the fuel injection quantity due tothe variation in the start time between in the case of referencein-cylinder pressure and in the case of in-cylinder pressure of theengine (i.e. the area within trapezoid Y on the left side of trapezoid Xin FIG. 15), the actual injection quantity Qr can be represented by thefollowing formula (1)Qr=Q−dQ 1+dQ 2  (1)

Therefore, a command value for attaining desired fuel injection isrepresented by the following formula (2).Q=Qr+dQ 1−dQ 2  (2)

In FIG. 15, letting A be the length of the upper base of trapezoid X, Bbe the length of the lower base of trapezoid X, Q′ be the height oftrapezoid X (i.e. the fuel injection rate in the case of referencein-cylinder pressure), q′ be the height of trapezoid Y and C be thelength of the portion of the upper base of trapezoid Y that overlapstrapezoid X, dQ1 is represented by the following formula (3)$\begin{matrix}\begin{matrix}{{dQ1} = {Q - q}} \\{= {Q - {\left( {B + C} \right){q^{\prime}/2}}}} \\{= {Q - {\left( {B + \left( {{{Aq}^{\prime}/Q^{\prime}} + {{B\left( {Q^{\prime} - q^{\prime}} \right)}/Q^{\prime}}} \right)} \right){q^{\prime}/2}}}} \\{= {{\left( {1 - {q^{\prime}/Q^{\prime}}} \right)Q} + {\left( {A - B} \right)\left( {q^{\prime} - Q^{\prime}} \right){q^{\prime}/Q^{\prime}}}}}\end{matrix} & (3)\end{matrix}$

In the conventional art, dQ2 in formula (2) is not taken intoconsideration, and corrected fuel injection rate is obtained by therelationship represented by the following formula (4).Qr=Qq′/Q′  (4)

Thus, in the conventional art, dQ1 is represented by the followingformula (5). $\begin{matrix}\begin{matrix}{{dQ1} = {Q - {Qr}}} \\{= {\left( {1 - {q^{\prime}/Q^{\prime}}} \right)Q}}\end{matrix} & (5)\end{matrix}$

Equation (5) lacks the second term in equation (3), and therefore, noconsideration has been given to an error corresponding to this term inthe conventional art.

In addition, when the rail pressure is low, the change in the fuelinjection rate after the start of the fuel injection is moderate.Therefore, the gradient of the left edge of the trapezoid is small andthe value (A–B) is large. Thus, in the case that the rail pressure islow, influence of the value (A–B) is significant, and therefore, a largeerror will be introduced if dQ1 is obtained from equation (5).

-   [Patent Document 1] Japanese Patent Application Laid-Open No.    9-256886-   [Patent Document 2] Japanese Patent Application Laid-Open No.    2000-54889

DISCLOSURE OF INVENTION

The present invention has been made in view of the above-describedsituation. An object of the present invention is to provide a technologyfor controlling the fuel injection quantity that changes with changes inthe in-cylinder pressure with improved accuracy.

In order to attain the above object, according to the present invention,there is provided a fuel injection control apparatus for an internalcombustion engine equipped with a fuel injection valve for directlyinjecting high pressure fuel supplied by high pressure fuel supply meansinto a cylinder, comprising:

-   -   in-cylinder pressure detection means for detecting or estimating        in-cylinder pressure of said cylinder;    -   time period calculation means for calculating fuel injection        time period over which fuel is injected from said fuel injection        valve, the fuel injection time period being corrected to        compensate a variation in the fuel injection quantity caused by        a variation in the fuel injection rate due to a variation in the        in-cylinder pressure detected or estimated by said in-cylinder        pressure detection means relative to a reference in-cylinder        pressure that is stored in advance;    -   start time variation calculation means for calculating a        variation in the fuel injection start time at the in-cylinder        pressure detected or estimated by said in-cylinder pressure        detection means relative to the fuel injection start time at        said reference in-cylinder pressure;    -   control means for controlling the time period over which fuel is        injected from said fuel injection valve based on the fuel        injection time period calculated by said time period calculation        means and the variation in the fuel injection start time        calculated by said start time variation calculation means.

By calculating a fuel injection time period while correcting a variationin the fuel injection quantity caused by a variation in the fuelinjection rate and calculating a variation in the fuel injection starttime, it is possible to control the fuel injection quantity that changeswith changes in the in-cylinder pressure with improved accuracy, and itis possible to attain a target fuel injection quantity irrespectively ofthe running state of the internal combustion engine.

The above-described apparatus may further include:

-   -   fuel pressure detection means for detecting the pressure of the        high pressure fuel supplied to said fuel injection valve by said        high pressure fuel supply means;    -   fuel injection quantity characteristic storing means for storing        a characteristic, in relation to valve opening time of said fuel        injection valve, of the fuel injection quantity injected by said        fuel injection valve during the valve opening time in accordance        with the pressure of the high pressure fuel supplied to said        fuel injection valve by said high pressure fuel supply means;    -   required fuel injection quantity calculation means for        calculating a desired fuel injection quantity based on the        running state of the internal combustion engine;    -   fuel injection rate calculation means for calculating fuel        injection rate based on the fuel pressure detected by said fuel        pressure detection means and the in-cylinder pressure detected        or estimated by said in-cylinder pressure detection means;    -   fuel injection quantity variation calculation means for        calculating a variation in the fuel injection quantity caused by        a variation in a second fuel injection rate calculated by said        fuel injection rate calculation means based on the in-cylinder        pressure detected or estimated by said in-cylinder pressure        detection means relative to a first fuel injection rate        calculated by said fuel injection rate calculation means based        on said reference in-cylinder pressure;    -   coefficient calculation means for calculating a variation in        fuel injection delay time per unit in-cylinder pressure for the        fuel pressure detected by said fuel pressure detection means.

In this case, said time period calculation means may calculate the fuelinjection time period utilizing said fuel injection quantitycharacteristic storing means based on the variation in the fuelinjection quantity calculated by said fuel injection quantity variationcalculation means and the fuel injection quantity calculated by saidrequired fuel injection quantity calculation means, and said start timevariation calculation means may calculate the variation in the fuelinjection start time based on a variation in the in-cylinder pressuredetected or estimated by said in-cylinder pressure detection meansrelative to said reference in-cylinder pressure and the variationcalculated by said coefficient calculation means.

With the above features, it is possible to calculate a correction valuebased on the reference in-cylinder pressure. Therefore, a characteristicstored in the fuel injection quantity characteristic storing means, forexample, a characteristic obtained by an injector characteristicsmeasuring benchmark test, can be applied to an actual internalcombustion engine directly.

The above-described apparatus may further includes:

-   -   a needle valve provided in said fuel injection valve that moves        in the axial direction to effect valve opening and closing        operations;    -   fuel injection quantity estimation means for estimating, when        fuel injection by said fuel injection valve is started, the        quantity of fuel injected since the valve opening operation of        said needle valve is started until said needle valve reaches a        full open state, based on the fuel pressure detected by said        fuel pressure detection means and the in-cylinder pressure        detected or estimated by said in-cylinder pressure detection        means;    -   comparison means for comparing the estimated fuel quantity        estimated by said fuel injection quantity estimation means and        the fuel injection quantity calculated by said required fuel        injection quantity calculation means,    -   wherein, said fuel injection quantity variation calculation        means may calculate the variation in the fuel injection quantity        using different calculation processes, in accordance with a        result of the comparison by said comparison means, between in        the case that said fuel injection quantity is less than said        estimated fuel quantity and in the case that said fuel injection        quantity is more than or equal to said estimated fuel quantity.

As per the above, by using different processes of calculating avariation in the fuel injection quantity depending on whether the needlevalve has reached the full open state or not, it is possible tocalculate the variation in the fuel injection quantity by a simplifiedcalculation method. Therefore, in the case that a relationship necessaryfor calculation of the variation in the fuel injection quantity isstored as a map, the data amount of the map can be made minimum.

In the above described apparatus, said fuel injection quantity variationcalculation means may calculate the variation in the fuel injectionquantity by modeling a change with time in the fuel injection rate as apolygon in a coordinate system and calculating a change in the area ofsaid polygon.

With this feature, it is possible to calculate the variation in the fuelinjection quantity more simply.

Furthermore, in the above-described apparatus, said fuel injectionquantity variation calculation means may include suction chamberpressure calculation means for calculating pressure in a suction chamberformed in the tip end side of a valve seat on/from which said needlevalve is to be received/detached, based on the fuel pressure detected bysaid fuel pressure detection means and the position of said needlevalve;

-   -   unit fuel injection quantity variation calculation means for        calculating a variation in the fuel injection quantity per unit        in-cylinder pressure based on the fuel injection quantity        calculated by said required fuel injection quantity calculation        means and the suction chamber pressure calculated by said        suction chamber pressure calculation means,    -   wherein, when according to a result of the comparison by said        comparison means, said fuel injection quantity is less than said        estimated fuel injection quantity, said fuel injection quantity        variation calculation means may calculate the variation in the        fuel injection quantity based on a variation in the in-cylinder        pressure detected or estimated by said in-cylinder pressure        detection means relative to said reference in-cylinder pressure        and the variation in the fuel injection quantity per unit        in-cylinder pressure calculated by said unit fuel injection        quantity variation calculation means.

With the above features, when the needle valve has not reached the fullopen state, the variation in the fuel injection quantity can becalculated based on the pressure of the suction chamber. Therefore,correction with improved accuracy can be made possible.

Still further, the above-described apparatus may further include:

-   -   fuel pressure detection means for detecting the pressure of the        high pressure fuel supplied to said fuel injection valve by said        high pressure fuel supply means;    -   fuel injection quantity characteristic storing means for storing        a characteristic, in relation to valve opening time of said fuel        injection valve, of the fuel injection quantity injected by said        fuel injection valve during the valve opening time in accordance        with the pressure of the high pressure fuel supplied to said        fuel injection valve by said high pressure fuel supply means;    -   required fuel injection quantity calculation means for        calculating a desired fuel injection quantity based on the        running state of the internal combustion engine;    -   first virtual fuel pressure calculation means for calculating a        first virtual fuel pressure by subtracting a variation in the        in-cylinder pressure detected or estimated by said in-cylinder        pressure detection means relative to said reference in-cylinder        pressure from the fuel pressure detected by said fuel pressure        detection means;    -   second virtual fuel pressure calculation means for calculating a        second virtual fuel pressure by adding a variation in the        in-cylinder pressure detected or estimated by said in-cylinder        pressure detection means relative to said reference in-cylinder        pressure to the fuel pressure detected by said fuel pressure        detection means;    -   injection delay time calculation means for calculating injection        delay time from the time at which a signal for opening said fuel        injection valve is generated to the time at which fuel injection        by said fuel injection valve is started, based on the fuel        pressure detected by said fuel pressure detection means,    -   wherein, said time period calculation means may calculate the        fuel injection time period utilizing said fuel injection        characteristic storing means based on the first virtual fuel        pressure calculated by said first virtual fuel pressure        calculation means and the fuel injection quantity calculated by        said required fuel injection quantity calculation means, and    -   said start time variation calculation means may calculate, by        means of said fuel injection delay time calculation means, a        fuel injection delay time for the fuel pressure detected by said        fuel pressure detection means and a fuel injection delay time        for the second virtual fuel pressure calculated by said second        virtual fuel pressure calculation means and calculates the        variation in the fuel injection start time from a difference        between those injection delay times.

By introducing a virtual fuel pressure as per the above, it is possibleto calculate the time period over which the fuel is injected in a moresimple way.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows the basic structure of a diesel engine as aninternal combustion engine in which a fuel injection control apparatusaccording to a first embodiment of the present invention is applied.

FIG. 2 is a cross sectional view schematically showing a fuel injectionvalve in the first embodiment of the present invention.

FIG. 3 is a block diagram showing the fuel injection control apparatusaccording to the first embodiment of the present invention.

FIG. 4 shows, in Part (A), a fuel injection rate changing behavior modelin which the changing behavior of the fuel injection rate is modeled asa trapezoid, and shows, in Part (B), a state in which the trapezoidshown in Part (A) is divided into two portions.

FIG. 5 is a diagram for illustrating a method of calculating a variationin the fuel injection quantity in the case that the fuel injection wascompleted before the needle valve reached the fully lifted state.

FIG. 6 is a diagram for illustrating correction of the variation in thefuel injection start time; Part (A) of FIG. 6 shows a relationshipbetween the driving signal and the fuel injection rate before thecorrection, and Part (B) of FIG. 6 shows a relationship between thedriving signal and the fuel injection rate after the correction.

FIG. 7 shows the relationship between the proportionality coefficient(or the sensitivity) a and the rail pressure Pcr in the first embodimentof the present invention.

FIG. 8 shows the relationship between variations in the fuel injectiondelay time Δτd and variations in the in-cylinder pressure ΔPcl.

FIG. 9 is a flow chart of a process of calculating correction value ofthe fuel injection quantity in the first embodiment of the presentinvention.

FIG. 10 is a block diagram showing fuel injection quantity variationcalculation means and related portions in the second embodiment of thepresent invention.

FIG. 11 is a block diagram showing a fuel injection control apparatusaccording to a third embodiment of the present invention.

FIG. 12 is a τ−Q map in the third embodiment of the present invention.

FIG. 13 shows the relationship between the rail pressure Pcr and thefuel injection delay time τd.

FIG. 14 is a graph showing a changing behavior of fuel injection rate.

FIG. 15 shows a fuel injection rate changing behavior model serving as amodel for the changing behavior of the fuel injection rate.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the best mode for carrying out the present inventionwill be described in detail based on exemplary embodiments.

Embodiment 1

FIG. 1 schematically shows the basic structure of a diesel engine as aninternal combustion engine in which a fuel injection control apparatusaccording to a first embodiment of the present invention is applied.

As shown in FIG. 1, the internal combustion engine 1 is mainly composedof a fuel supply system 2, cylinders (or combustion chambers) 3, intakepassage 4 and exhaust passage 5. The internal combustion engine 1 is anin-line four cylinder diesel engine in which four cycles includingintake stroke, compression stroke, explosion stroke (or expansionstroke) and exhaust stroke are repeated to create an output.

The fuel supply system 2 includes a supply pump 6, a common rail 7, fuelinjection valves 8, fuel passage 9 etc. The supply pump 6 raises thepressure of the fuel drawn from a fuel tank (not shown) to a highpressure and supplies the fuel to the common rail 7 through the fuelpassage 9. The common rail 7 functions as a pressure accumulationchamber for maintaining (or accumulating) the pressure of high pressurefuel supplied from the supply pump 6 at a predetermined pressure anddistributes the pressurized fuel to the respective fuel injection valves8 through the fuel pipes connected to the common rail 7. The highpressure fuel supply means comprises the supply pump 6, the common rail7 and the fuel passage 9.

The fuel injection valve 8 is an electromagnetically driven on-off valveequipped with a electromagnetic solenoid (not shown) in the interiorthereof. The fuel injection valve 8 is opened fitly to supply anappropriate quantity of the fuel pressurized in the common rail 7 intothe interior of the cylinder 3 by direct injection at an appropriatetiming. The fuel injection valve 8 may be equipped with a piezoelectricactuator instead of the electromagnetic solenoid.

The internal combustion engine 1 is provided with various sensors suchas an accelerator position sensor that outputs a signal indicative ofthe travel of the accelerator pedal (not shown) resulting fromdepression by the driver, a crank position sensor that outputs a signalindicative of the number of engine revolutions of the crankshaft (notshown), a water temperature sensor that outputs a signal indicative ofthe temperature of cooling water circulating in the internal combustionengine 1 (the cooling water temperature), an air flow meter outputting asignal indicative of the flow rate of the air introduced into thecylinder 3 through the intake passage 4 (the intake air quantity) and arail pressure sensor 11 that detects the pressure of the high pressurefuel under pressure in the common rail 7 (the rail pressure). Thesignals of these sensors are input to an electronic control unit (ECU)10. The rail pressure sensor 11 constitutes the fuel pressure detectionmeans.

ECU 10 includes a logical operating circuit composed of a centralprocessing unit (CPU), a read only memory (ROM), a random access memory(RAM), a backup RAM and other elements. The ECU 10 performs overallcontrol of various components of the internal combustion engine 1 basedon signals from various sensors. For example, the ECU 10 detects therunning state of the internal combustion engine 1 to control theopening/closing operation of the fuel injection valves 8.

Furthermore, the ECU 10 executes inputting of signals output fromvarious sensors, calculation of the number of engine revolutions,calculation of the load, calculation of the fuel injection quantity etc.in a basic routine that is to be performed at regular intervals. Varioussignals input into the ECU 10 and various control values obtainedthrough the calculation by the ECU 10 in the basic routine aretemporarily stored in the RAM of the ECU 10. Still further, in aninterrupting process that is triggered by, for example, signal inputsfrom various sensors or switches, lapse of a certain time or input of apulse signal from a crank position sensor, the ECU 10 reads out variouscontrol values from the RAM and executes the fuel injection control orother control in accordance with those control values. The ECU 10constitutes the fuel injection control apparatus, and constitutes thetime period calculation means 51, the start time variation calculationmeans 52, the control means 53, the fuel injection quantitycharacteristic storing means 54, the required fuel injection quantitycalculation means 55, the fuel injection rate calculation means 56, thefuel injection quantity variation calculation means 57, the coefficientcalculation means 58, the fuel injection quantity estimation means 59and comparison means 60 in FIG. 3 described hereinafter.

In the following, the fuel injection valve 8 will be more specificallydescribed. FIG. 2 is a cross sectional view schematically showing thefuel injection valve 8 in this embodiment.

As shown in FIG. 2, the fuel injection valve 8 includes a main body 22having a fuel injection hole 21 at its tip end, a needle-shaped needlevalve 23 (i.e. the valve body) and a coil spring 24 that biases theneedle valve 23 in the closing direction. The needle valve 23 isdisposed in the interior of the main body 22 in such a way as to bemovable in the axial direction. The needle valve 23 closes the fuelinjection hole 21 when received on a valve seat 25 in its advanced stateand opens the fuel injection valve 21 when detached from the valve seat25 in its retracted state. The fuel injection hole 21 is provided at asuction chamber 26 provided in the tip end side of the valve seat 25 inthe main body 22.

Furthermore, the fuel injection valve 8 includes a first fuel supplypassage 31 for introducing high pressure fuel supplied from the commonrail 7 with a predetermined pressure to the fuel injection hole 21, acontrol chamber 32 for receiving high pressure fuel to press the needlevalve 23 in the closing direction, a second fuel supply passage 33branching from the first fuel supply passage 31 for introducing highpressure fuel supplied from the common rail 7 with a predeterminedpressure to a control chamber 32 and a fuel discharge passage 34 fordischarging the high pressure fuel in the control chamber 32 to reducethe fluid pressure in the control chamber 32.

In the second fuel supply passage 33, an inlet orifice 33 a thatdetermines the flow rate of the fuel flowing into the control chamber 32is provided. In the fuel discharge passage 34, an outlet orifice 34 athat determines the fuel discharge amount is provided. The ratio of thecross sectional area of the inlet orifice 33 a and the outlet orifice 34a is designed in such a way that the cross sectional area of the outletorifice 34 a is larger than that of the inlet orifice 33 a. For example,the ratio is 2:3.

The needle valve 23 has a main piston 23 a that faces the controlchamber 32 and receives the fuel pressure in the control chamber 32 tomove the needle valve 23 downwardly. A sub piston 23 c is provided inthe fuel injection hole 21 side of the needle valve 23 relative to themain piston 23 a. At a position in the first fuel supply passage 31leading to the fuel injection hole 21, there is provided a fuelreservoir 31 a in such a way as to face the sub piston 23 c. Thus, thepressure of the fuel in the fuel reservoir 31 a acts on the sub piston23 c to press the needle valve 23 in the opening direction (i.e. theupward direction in FIG. 2). The area Ss over which the sub piston 23 creceives the pressure of the fuel in the fuel reservoir 31 a is designedto be smaller than the area Sm over which the main piston 23 a receivesthe pressure of the fuel in the control chamber 32. In addition, a coilspring 24 for biasing the needle valve 23 in the closing direction isprovided in the main piston 23 a side of the sub piston 23 c.

Letting Fm be the pressing force exerted on the main piston 23 a by thepressure of the fuel in the control chamber 32, Fs be the pressing forceexerted on the sub piston 23 c by the pressure of the fuel in the fuelreservoir 31 a, Fc be the biasing force of the coil spring 24,inequalities Fm+Fc>Fs and Fc<Fs hold in the steady state.

Furthermore, a back pressure control valve 35 for sealing, in its closedstate, high pressure fuel in the control chamber 32 and for letting, inits opened state, fuel out of the control chamber 32 to the fueldischarge passage 34 is provided intervening in the fuel dischargepassage 34 from the control chamber 32. The back pressure control valve35 is composed of an electromagnetic valve and provide in the interiorof the main body 22. When the back pressure control valve 35 is in theclosed state, the pressure of the fuel in the control chamber 32increases to press the main piston 23 a to move the needle valve 23downwardly in cooperation with the biasing force of the coil spring 24.

In this process, although fuel having the pressure same as the pressurein the control chamber 32 is introduced from the first fuel supplypassage 31 into the fuel reservoir 31 a to press the sub piston 23 c,its pressing force Fs cannot match the cooperative force Fm+Fc.Consequently, the needle valve 23 is maintained in the state in which itcloses the fuel injection hole 21.

After that, when the back pressure control valve 35 is opened, fuel isdischarged from the control chamber 32 through the fuel dischargepassage 34. In this process, since the outlet orifice 34 a is designedto be larger than the inlet orifice 33 a, the quantity of the fuelflowing out of the control chamber 32 is more than the quantity of thefuel flowing into the control chamber 32. Consequently, the fuelpressure in the control chamber 32 falls.

Then at the time when Fm+Fc<Fs is established, the needle valve 23 lifts(i.e. moves upward, and opens the valve), so that the fuel injectionhole 21 is opened and the fuel injection is started.

Here, a fuel injection valve drive control process for driving the fuelinjection valve 8 will be described. The fuel injection valve drivecontrol process is executed by the ECU 10.

Before fuel injection, the ECU 10 keeps the back pressure control valve35 in the closed state, and the interior of the control chamber 32 isfilled with high pressure fuel introduced from the common rail 7 throughthe second fuel supply passage 33. Thus, the piston 23 a of the needlevalve 23 is in the lowered position and the fuel injection hole 21 isclosed.

When the time for fuel injection comes, the back pressure control valve35 is opened by a command from the ECU 10, and high pressure fuel in theinterior of the control chamber 32 is discharged through the fueldischarge passage 34. Consequently, the fuel pressure in the controlchamber 32 falls, so that the needle valve 23 lifts to open the fuelinjection hole 21.

When a predetermined fuel injection time elapses after that, the backpressure valve 35 is closed by the ECU 10. Then, high pressure fuelflows into the control chamber 32 and is sealed therein. Thus, thepressure in the control chamber 32 rises, so that the needle valve 23goes down to close the fuel injection hole 21.

FIG. 3 is a block diagram of the fuel injection control apparatusaccording to this embodiment. As shown in FIG. 3, the fuel injectioncontrol apparatus according to this embodiment is equipped with a timeperiod calculation means 51, start time variation calculation means 52and control means 53.

The time period calculation means 51 calculates the fuel injection timeperiod being corrected to compensate a variation in the fuel injectionquantity caused by a variation in the fuel injection rate due to avariation in the in-cylinder pressure detected or estimated by thein-cylinder pressure detection means 61 relative to a referencein-cylinder pressure that is stored in advance.

The start time variation calculation means 52 calculates a variation inthe fuel injection start time at the in-cylinder pressure detected orestimated by in-cylinder pressure detection means 61 relative to thefuel injection start time at the reference in-cylinder pressuredescribed later.

The control means 53 controls the time period over which fuel isinjected from the fuel injection valve 8 based on the fuel injectiontime period calculated by the time period calculation means 51 and thevariation in the fuel injection start time calculated by the start timevariation calculation means 52.

The fuel injection control apparatus according to this embodiment isfurther equipped with the fuel injection quantity characteristic storingmeans 54 for storing a characteristic, in relation to valve opening timeof the fuel injection valve 8, of the fuel injection quantity injectedby the fuel injection valve 8 during the valve opening time inaccordance with the pressure of the high pressure fuel supplied to thefuel injection valve 8; the required fuel injection quantity calculationmeans 55 for calculating a desired fuel injection quantity based on therunning state of the internal combustion engine; the fuel injection ratecalculation means 56 for calculating fuel injection rate based on thefuel pressure detected by the rail pressure sensor 11 and thein-cylinder pressure detected or estimated by the in-cylinder pressuredetection means 61; the fuel injection quantity variation calculationmeans 57 for calculating a variation in the fuel injection quantitycaused by a variation in a second fuel injection rate calculated by thefuel injection rate calculation means 56 based on the in-cylinderpressure detected or estimated by the in-cylinder pressure detectionmeans 61 relative to a first fuel injection rate calculated by the fuelinjection rate calculation means 56 based on the reference in-cylinderpressure; the coefficient calculation means 58 for calculating avariation in fuel injection delay time per unit in-cylinder pressure forthe fuel pressure detected by the rail pressure sensor 11.

The time period calculation means 51 calculates the fuel injection timeperiod utilizing the fuel injection quantity characteristic storingmeans 54 based on the variation in the fuel injection quantitycalculated by the fuel injection quantity variation calculation means 57and the fuel injection quantity calculated by the required fuelinjection quantity calculation means 55.

The start time variation calculation means 52 calculates the variationin the fuel injection start time based on a variation in the in-cylinderpressure detected or estimated by the in-cylinder pressure detectionmeans 61 relative to the reference in-cylinder pressure and thevariation calculated by the coefficient calculation means 58.

Furthermore, the fuel injection quantity estimation means 59 estimatesthe quantity of fuel injected since the valve opening operation of theneedle valve 23 is started until the needle valve 23 reaches a full openstate, based on the fuel pressure detected by the rail pressure sensor11 and the in-cylinder pressure detected or estimated by the in-cylinderpressure detection means 61.

The comparison means 60 compares the estimated fuel quantity estimatedby the fuel injection quantity estimation means 59 and the fuelinjection quantity calculated by the required fuel injection quantitycalculation means 55.

The fuel injection quantity variation calculation means 57 calculatesthe variation in the fuel injection quantity using different calculationprocesses, in accordance with a result of the comparison by thecomparison means 60, between in the case that said fuel injectionquantity is less than the estimated fuel quantity and in the case thatsaid fuel injection quantity is more than or equal to the estimated fuelquantity.

In the following, a method of correcting the fuel injection quantitywill be described in particular.

In the case that fuel is directly injected into the cylinder 3 by thefuel injection valve 8, the in-cylinder pressure serving as the backpressure changes in accordance with the running state of the engine.Therefore, even if the ECU 10 commands to inject a predeterminedquantity of fuel, variations are generated in the actual fuel injectionquantity.

The internal combustion engine 1 is a direct injection internalcombustion engine equipped with the fuel injection valve 8 for injectingfuel into the cylinder directly, and so the fuel injection hole 21 isdisposed in the interior of the cylinder 3. When the fuel injection hole21 is opened, as described above, the back pressure control valve 35 isopened by a command from the ECU 10 and high pressure fuel in theinterior of the control chamber 32 is discharged through the fueldischarge passage 34. Thus, the fuel pressure in the control chamber 32falls, so that the needle valve 23 will lift. In this process, since thefuel injection hole 21 is disposed in the interior of the cylinder 3,the in-cylinder pressure is exerted on the needle valve 23. Since thein-cylinder pressure acts on the needle valve 23 in the liftingdirection, the opening timing of the fuel injection hole 21 is advanced,namely the fuel injection is started at an earlier time.

In view of this, in this embodiment, a variation in the fuel injectionquantity caused by a variation in the fuel injection rate at thein-cylinder pressure of the engine (a detected or estimated pressure inthe running state of the internal combustion engine) relative to thefuel injection rate at a reference in-cylinder pressure (for example,the condition in an injector characteristics measuring benchmark test(e.g. 1 Mpa)) is calculated (or estimated) and, in addition, a variationin the fuel injection start time is corrected to control the powersupply time during which electric power is supplied to the fuelinjection valve 8 (i.e. to the back pressure control valve 3) (namely,the time period over which fuel is injected by the fuel injection valve8) is controlled. In other words, the time period over which fuel isinjected from the fuel injection valve 8 is controlled by the controlmeans 53 based on the fuel injection time period calculated by the timeperiod calculation means 51 and the variation in the fuel injectionstart time calculated by the start time variation calculation means 52.

Firstly, a method for calculating a variation in the fuel injectionquantity due to a variation in the fuel injection rate will bedescribed.

In this embodiment, a fuel injection rate changing behavior model inwhich the changing behavior of the fuel injection rate is modeled in asimilar manner as FIG. 15 that was referred to in the description ofbackground arts is used (see FIG. 4), and correction of the fuelinjection quantity is performed utilizing the fuel injection ratechanging behavior model.

In addition, in this embodiment, the calculation process is switcheddepending on whether the lifting distance (moving distance) of theneedle valve 23 reaches one of the fully lifted states (the position atwhich the needle valve 23 lifts (opens) completely or is in the fullyopened state) or not, Wherein, the needle valve 23 lifts in accordancewith the desired fuel injection quantity (requested fuel injectionquantity) based on the running condition of the engine.

In other words, the calculation process is switched between in the casein which the fuel injection was effected after or at the same time whenthe needle valve 23 had reached the fully lifted state and in the casein which the execution of the fuel injection was completed before theneedle valve 23 had reached the fully lifted state. In connection withthis, determination as to whether the needle valve had reached the fullylifted state is made by comparing a fuel injection quantity calculatedby the required fuel injection quantity calculation means 55 and anestimated fuel quantity calculated by the fuel injection quantityestimation means 59 (a fuel quantity supposed to be injected until theneedle valve 23 reaches the fully lifted state, which is estimated basedon the fuel pressure detected by the rail pressure sensor 11 and thein-cylinder pressure detected or estimated by the in-cylinder pressuredetection means 61 (which will be described later)) by the comparisonmeans 60. Based on the result of the comparison by the comparison means60, a variation in the fuel injection quantity is calculated usingcalculation process that is different between in the case in which thefuel injection quantity is less than or equal to the estimated fuelquantity and in the case in which the fuel injection quantity is morethan the estimated fuel quantity. In the following both of the abovecases will be described.

First, a description will be made on the case in which the fuelinjection was effected after or at the same time when the needle valve23 had reached the fully lifted state.

Part (A) in FIG. 4 shows a fuel injection rate changing behavior modelin which the changing behavior of the fuel injection rate is modeled asa trapezoid. Part (B) of FIG. 4 shows a state in which the trapezoidshown in Part (A) in FIG. 4 is divided into two portions.

In FIG. 4, trapezoid X shown by the solid line is a model for the fuelinjection rate waveform X (in the case of reference in-cylinderpressure) shown in FIG. 14, as with FIG. 15, and trapezoid Y shown bythe broken line is a model for the fuel injection rate waveform Y (inthe case of the engine in-cylinder pressure) shown in FIG. 14.

Position (coordinates) a shown in FIGS. 4(A) and 4(B) is set torepresent the fuel injection rate at the time when the needle valve 23reaches the fully lifted state. An additional line is drawn from thisposition a parallel to the right edge of trapezoid X, so that thetrapezoid X is divided into a triangle X1 and a parallelogram X2 asshown in Part (B) in FIG. 4

Here, as shown in FIGS. 4(A) and 4(B), the vertexes of trapezoid X aredesignated by a, b, c and d, and the vertexes of trapezoid Y aredesignated by e, f, g and h. In addition the intersection point of theleft edge ab of trapezoid X and the upper base eh of trapezoid Y isdesignated by i, the intersection point of the additional line drawnfrom vertex a parallel to the right edge dc and the lower base bc isdesignated by j, and the intersection point of the left edge aj ofparallelogram X2 and the upper base eh of trapezoid Y is designated byk.

The variation ΔQ in the fuel injection quantity with a change in thefuel injection rate is calculated by the following equation (6). Here,the variation ΔQ of the fuel injection quantity with a change in thefuel injection rate corresponds to the area of trapezoid aihd. Thevariation ΔQ of the fuel injection quantity can be represented as thesum of the variation Δq1 until the needle valve 23 reaches the fullylifted state (the area of triangle aik) and the variation Δq2 after theneedle valve has reached the fully lifted state (the area ofparallelogram akhd).

Namely, the variation ΔQ in the fuel injection quantity is representedas follows.ΔQ=Δq 1+Δq 2  (6)

Here, the fuel injection quantity at the time when the needle valve 23reached the fully lifted state, or the area of triangle abj isrepresented by Qfl, the required fuel injection quantity, or the area oftrapezoid X is represented by Q, the fuel injection rate at thereference in-cylinder pressure, or the height of trapezoid X isrepresented by Q′, and the fuel injection rate at the in-cylinderinjection, or the height of trapezoid Y is represented by q′. Then, theheight of triangle aik and parallelogram akhd is represented by (Q′−q′)and the area of parallelogram ajcd is represented by (Q−Qfl). Therefore,the variations Δq1 and Δq2 can be calculated by the following formulas(7) and (8) based on the ratio of the areas.Δq 1=Qfl×(1−q′/Q′)²  (7)Δq 2=(Q−Qfl)×(1−q′/Q′)  (8)

Here, the fuel injection rate can be interpreted as an orifice flow, andthe fuel injection rates Q′ and q′ can be calculated by the followingformulas (9) and (10) respectively. In connection with this, the orificecoefficient is represented by CO, the injection hole area (i.e. the areaof the aperture of the fuel injection valve) is represented by A, therail pressure is represented by Pcr, the in-cylinder pressure at thetime of starting the fuel injection is represented by Pcl, the referencein-cylinder pressure is represented by P0 and the density of the fuel isrepresented by ρ.Q′=C 0×A×(2×(Pcr−P 0)/ρ)^(1/2)  (9)q′=C 0×A×(2×(Pcr−Pcl)/ρ)^(1/2)  (10)

Therefore, the variation ratio (q′/Q′) of the fuel injection rate can berepresented by the following formula (11).q′/Q′=((Pcr−Pcl)/(Pcr−P 0))^(1/2)  (11)

In the case that the fuel injection is effected after or at the sametime when the needle valve 23 has reached the fully lifted state, avariation ΔQ in the fuel injection quantity caused by a change in thefuel injection rate can be calculated by the above-described method.

Next, a description will be made of the case in which the fuel injectionwas completed before the needle valve 23 reached the fully lifted state.

FIG. 5 is a diagram for illustrating a method of calculating a variationin the fuel injection quantity in the case that the fuel injection wascompleted before the needle valve 23 reached the fully lifted state.

In FIG. 5, triangle X1 is a model for the waveform of the fuel injectionrate at the time when the needle valve 23 reached the fully lifted stateas with triangle X shown in Part (B) in FIG. 4. The hatched triangle X1′is a model for the waveform of the fuel injection rate in the case thatthe fuel injection was completed before the needle valve 23 had reachedthe fully lifted state.

The variation ΔQ1 in the fuel injection quantity in the case that thefuel injection was completed before the needle valve 23 reached thefully lifted state can be obtained based on the ratio of the area oftriangle X1 and the area of triangle X1′.

The areas of triangle X1 is represented by Qfl, and the area of triangleX1′ corresponds to the fuel injection quantity Q as described above.Thus, the ratio of the areas is represented by the following formula(12).ΔQ 1/Δq 1=Q/Qfl  (12)

Therefore, the variation ΔQ1 in the fuel injection quantity in the casethat the fuel injection was completed before the needle valve 23 reachedthe fully lifted state can be represented by the following formula (13).ΔQ 1=Q×(1−q′/Q′)²  (13)

Next, correction of the variation in the fuel injection start time willbe described.

FIG. 6 is a diagram for illustrating the correction of the variation inthe fuel injection start time. Part (A) of FIG. 6 shows the relationshipbetween the driving signal and the fuel injection rate before thecorrection. Part (B) of FIG. 6 shows the relationship between thedriving signal and the fuel injection rate after the correction. In bothPart (A) and Part (B) of FIG. 6, the upper curve represents the drivingsignal and the lower curve represents the fuel injection rate. In part(A) of FIG. 6 also, the waveform X of the fuel injection rate at thereference in-cylinder pressure is shown by the solid line and thewaveform Y of the fuel injection rate at the in-cylinder pressure of theengine is shown by the broken line, in a similar manner as in FIG. 4.Reference signs b and f in Part (A) of FIG. 6 correspond to referencesigns b and f in Part (A) of FIG. 4 respectively.

As will be seen from Part (A) of FIG. 6, in the case of the referencein-cylinder pressure, there is a time delay τd1 before the fuelinjection is started after generation of the fuel injection signal bythe ECU 10. On the other hand, in the case of the in-cylinder injection,there is a time delay τd2 before the fuel injection is started aftergeneration of the fuel injection signal, namely, the fuel injection isstarted earlier than in the case of reference in-cylinder pressure by atime Δτd (=τd1−τd2). In the following, time τd1 or τd2 will be sometimesreferred to as the fuel injection delay time id.

It is already known that the time id is substantially proportional tothe variation in the in-cylinder pressure and the proportionalitycoefficient (i.e. the sensitivity of the variation of the fuel injectiondelay time id) a varies depending on the rail pressure Pcr. Theirrelationship is shown in FIGS. 7 and 8. FIG. 7 shows the relationshipbetween the proportionality coefficient (or the sensitivity) a and therail pressure Pcr (specifically, the variation in the fuel injectiondelay time per unit in-cylinder pressure relative to the rail pressure).FIG. 8 shows the relationship between the variation in the fuelinjection delay time id (time Δτd) and the variation in the in-cylinderpressure ΔPcl (=Pcl(engine in−cylinder pressure)−Pcl′ (referencein-cylinder pressure)).

Thus, Δτd can be obtained from the following formula (14) by calculatingthe rail pressure Pcr and the variation in the in-cylinder pressure(Pcl−Pcl′). In connection with this, it is preferable that therelationship between the rail pressure Pcr and the proportionalitycoefficient α be prepared as a map in advance. Such a map constitutesthe coefficient calculation means 58.Δτd=α×(Pcl−Pcl′)  (14)

As shown in Part (B) of FIG. 6, it is possible to correct a change inthe fuel injection quantity caused by a change in the fuel injectionstart time by shortening a signal for opening the fuel injection valve 8by time Δτd obtained by formula (14). Furthermore, it is possible tocorrect the fuel injection timing, which may be made earlier by theinfluence of in-cylinder pressure, to a desired fuel injection timing bydelaying the fuel injection timing by Δτd.

As described above, according to the present invention, it is possibleto calculate the variation in the fuel injection quantity caused by achange in the fuel injection rate and to calculate the variation in thefuel injection start time. In the following, a process of controllingthe power supply time over which electric power is supplied to the fuelinjection valve 8 in order to open the fuel injection valve 8 will bedescribed.

FIG. 9 is a flow chart for illustrating a process of calculating acorrection value for the fuel injection quantity.

Firstly, in step S101, a required fuel injection quantity is read by theECU 10 in accordance with the running state of the internal combustionengine 1. This corresponds to calculation of a required fuel injectionquantity by the required fuel injection quantity calculation means 55.

Next in step S102, the in-cylinder pressure (the in-cylinder pressure ofthe engine) at the time when the fuel injection is started iscalculated. The calculation of the in-cylinder pressure may beimplemented by directly detecting the in-cylinder pressure by detectionmeans provided for detecting the pressure in the cylinder 3 or byestimating the in-cylinder pressure. The in-cylinder pressure can beestimated based on, for example, the pressure in the intake passage 4and the ratio of the interior volume of the cylinder (i.e. the ratio ofthe volume during the fuel injection and the volume at the bottom deadcenter). This corresponds to detection of the in-cylinder pressure ofthe cylinder 3 by the in-cylinder pressure detection means 61.

Next in step S103, the ratio of variation of the fuel injection rate iscalculated. The ratio of variation of the fuel injection rate iscalculated by formula (11) presented before. This corresponds tocalculation of the fuel injection rate by the fuel injection ratecalculation means 56.

Next in step S104, the variation in the fuel injection quantity (or thecorrection value for the variation in the fuel injection rate) caused bya change in the fuel injection rate is calculated. This corresponds tocalculation of the variation in the fuel injection quantity by the fuelinjection quantity variation calculation means 57. This calculation isperformed in accordance with the above-described method (calculationusing formula (6) and formula (13)), and its result is taken into a stepof determining a final designated fuel injection quantity that isexecuted in another routine. This step will be referred to as step S201for facilitating description. In step S201, a final designated fuelinjection quantity is calculated by correcting the required fuelinjection quantity based on the variation in the fuel injection quantitycalculated in step S104.

In step S105 succeeding step S104, the variation in the fuel injectionstart time is calculated by the start time variation calculation means52. This calculation is executed in accordance with the above-describedmethod, and its result is taken into a step of determining a final powersupply time that is executed in another routine. This step will bereferred to as step S202 to facilitating description.

In step S202, a power supply time is calculated based on the requiredfuel injection quantity after correction calculated in step S201 and thepower supply time is corrected based on the variation in the fuelinjection start time calculated in step S105. Thus, the final powersupply time is determined.

Here, it is preferable that the relationship between the power supplytime (i.e. the time period τ during which the fuel injection valve 8 isopened) and the fuel injection quantity (Q) be obtained in advance byexperiments and prepared as a τ−Q characteristic in the form of a map.The power supply time can be calculated based on the required fuelinjection quantity after correction using that τ−Q map. Then, it ispossible to determine the final power supply time by increasing ordecreasing the power supply time by a value corresponding to thevariation in the fuel injection start time. The aforementioned mapconstitutes the fuel injection quantity characteristic storing means 54.

Fuel injection with an accurate quantity can be attained by applying thefinal power supply time thus determined as power supply time to the fuelinjection valve 8. It should be understood that no limitation is placedon the type of the above-described fuel injection valve 8 and thisembodiment can be preferably applied to an injection valve driven by asolenoid and an injection valve driven by a piezoelectric element. Inaddition, this embodiment can be preferably applied to a direct driveinjection valve having no control chamber by setting the variation inthe fuel injection delay time τd as 0 (no variation).

Embodiment 2

In the second embodiment of the present invention, in the case thatexecution of the fuel injection is completed before the lift amount ofthe needle valve 23 reaches the full lift, the fuel injection quantityis corrected in accordance with a method different from the methoddescribed in connection with the first embodiment. FIG. 10 is a blockdiagram showing the fuel injection quantity variation calculation means57 and related portions in this embodiment. In this embodiment, the ECU10 constitutes the suction chamber pressure calculation means 57 a andthe unit fuel injection quantity variation calculation means 57 b.

The fuel injection quantity variation calculation means 57 is equippedwith a suction chamber pressure calculation means 57 a for calculatingpressure in a suction chamber 26 formed in the tip end side of a valveseat on/from which the needle valve 23 is to be received/detached, basedon the fuel pressure detected by the rail pressure sensor 11 and theposition of said needle valve 23; the unit fuel injection quantityvariation calculation means 57 b for calculating a variation in the fuelinjection quantity per unit in-cylinder pressure based on the fuelinjection quantity calculated by the required fuel injection quantitycalculation means 55 and the suction chamber pressure calculated by thesuction chamber pressure calculation means 57 a.

When according to a result of the comparison by the comparison means 60,the fuel injection quantity is less than the estimated fuel injectionquantity, the fuel injection quantity variation calculation means 57calculates the variation in the fuel injection quantity based on avariation in the in-cylinder pressure detected or estimated by thein-cylinder pressure detection means 61 relative to the referencein-cylinder pressure and the variation in the fuel injection quantityper unit in-cylinder pressure calculated by the unit fuel injectionquantity variation calculation means 57 b.

The basic structure of the internal combustion engine of this embodimentis the same as that in the first embodiment, and the parts in thisembodiment same as those in the first embodiment will be designated bythe same reference signs and descriptions thereof will be omitted.

In the case that the needle valve 23 does not reach the fully liftedstate, especially in the case that fuel injection is effected in thestate with a small lift amount, the actual pressure in the fuelinjection process (the actual injection pressure) does not reach therail pressure. In view of this, in this embodiment, the fuel injectionquantity is corrected based on the pressure in the suction chamber 26 orthe so-called suction chamber pressure (namely, the pressure actuallyapplied to the injection hole (equivalent to the actual injectionpressure)).

The suction chamber pressure is determined by the lift position of theneedle valve 23 and the actual rail pressure detected by the railpressure sensor 11. The lift position of the needle valve 23 isdetermined by the time and the lifting speed of the needle valve 23. Thelifting speed of the needle valve 23 can be determined based on thecharacteristics of the orifice flow flowing out of the control camber 32through the outlet orifice 34 a. The movement can be assumed to beuniform motion, that is the lifting speed of the needle valve 23 can beassume to be substantially constant. Therefore, the suction chamberpressure can be represented as a function of the time, and it can beobtained based on the time. This corresponds to calculation of thepressure in the suction chamber 26 by the suction chamber pressurecalculation means 57 a.

Thus, if a map for obtaining the variation in fuel injection quantityper unit in-cylinder pressure based on the required fuel injectionquantity calculated by the required fuel injection quantity calculationmeans 55 and the suction chamber pressure is prepared in advance by, forexample, experiments, it is possible to calculate the variation in thefuel injection quantity based on the variation in fuel injectionquantity per unit in-cylinder pressure and the variation in thein-cylinder pressure of the engine relative to the reference in-cylinderpressure. The aforementioned map constitutes the unit fuel injectionquantity variation calculation means 57 b.

According to this embodiment, since in the case that the fuel injectionis completed before the lift amount of the needle valve 23 reaches thefull lift, a correction value is calculated based on the suction chamberpressure that is equivalent to the actual injection pressure, correctionwith improved accuracy can be realized. In connection with this process,determination as to whether the execution of the fuel injection iscompleted before the lift amount of the needle valve 23 reaches the fulllift or not is determined based on the result of the comparison effectedby the comparison means 60.

Embodiment 3

In the third embodiment of the present invention, correction of the fuelinjection quantity is performed based on the rail pressure Pcr and thein-cylinder pressure of the engine Pcl, unlike with the firstembodiment. Specifically, when the in-cylinder pressure of the enginePcl increases, it is assumed that the rail pressure Pcr has decreased,and fuel injection time is calculated while compensating the variationin the fuel injection quantity due to a change in the fuel injectionrate based on the difference between the rail pressure Pcr and thein-cylinder pressure of the engine Pcl. In addition, when thein-cylinder pressure of the engine Pcl increases, it is assumed that therail pressure Pcr has increased, and variation in fuel injection starttime is calculated based on the sum of the rail pressure Pcr and thein-cylinder pressure of the engine Pcl.

FIG. 11 is a block diagram of the fuel injection control apparatus inthis embodiment.

As shown in FIG. 11, the fuel injection control apparatus according tothis embodiment is equipped with the time period calculation means 51,start time variation calculation means 52 and control means 53.

The time period calculation means 51 calculates the fuel injection timeperiod being corrected to compensate a variation in the fuel injectionquantity caused by a variation in the fuel injection rate due to avariation in the in-cylinder pressure detected or estimated by thein-cylinder pressure detection means 61 relative to a referencein-cylinder pressure that is stored in advance.

The start time variation calculation means 52 calculates a variation inthe fuel injection start time at the in-cylinder pressure detected orestimated by in-cylinder pressure detection means 61 relative to thefuel injection start time at the reference in-cylinder pressuredescribed later.

The control means 53 controls the time period over which fuel isinjected from the fuel injection valve 8 based on the fuel injectiontime period calculated by the time period calculation means 51 and thevariation in the fuel injection start time calculated by the start timevariation calculation means 52.

The fuel injection control apparatus according to this embodiment isfurther equipped with the rail pressure sensor 11 for detecting thepressure of the high pressure fuel supplied to the fuel injection valve8; the fuel injection quantity characteristic storing means 54 forstoring a characteristic, in relation to valve opening time of the fuelinjection valve 8, of the fuel injection quantity injected by the fuelinjection valve 8 during the valve opening time in accordance with thepressure of the high pressure fuel supplied to the fuel injection valve8; the required fuel injection quantity calculation means 55 forcalculating a desired fuel injection quantity based on the running stateof the internal combustion engine; the first virtual fuel pressurecalculation means 65 for calculating a first virtual fuel pressure bysubtracting a variation in the in-cylinder pressure detected orestimated by the in-cylinder pressure detection means 61 relative to thereference in-cylinder pressure from the fuel pressure detected by therail pressure sensor 11; the second virtual fuel pressure calculationmeans 66 for calculating a second virtual fuel pressure by adding avariation in the in-cylinder pressure detected or estimated by thein-cylinder pressure detection means 61 relative to the referencein-cylinder pressure to the fuel pressure detected by the rail pressuresensor 11; the injection delay time calculation means 67 for calculatinginjection delay time from the time at which a signal for opening thefuel injection valve 8 is generated to the time at which fuel injectionby the fuel injection valve 8 is started, based on the fuel pressuredetected by the rail pressure sensor 11.

The time period calculation means 51 calculates the fuel injection timeperiod utilizing the fuel injection quantity characteristic storingmeans 54 based on the first virtual fuel pressure calculated by thefirst virtual fuel pressure calculation means 65 and the fuel injectionquantity calculated by the required fuel injection quantity calculationmeans 55.

The start time variation calculation means 52 calculates, by means ofthe fuel injection delay time calculation means 67, a fuel injectiondelay time for the fuel pressure detected by the rail pressure sensor 11and a fuel injection delay time for the second virtual fuel pressurecalculated by the second virtual fuel pressure calculation means 66 andcalculates the variation in the fuel injection start time from adifference between those injection delay times.

In this embodiment, the ECU 10 constitutes the first virtual fuelpressure calculation means 65, the second virtual fuel pressurecalculation means 66 and the injection delay time calculation means 67.The basic structure of the internal combustion engine 1 of thisembodiment is the same as that in the first embodiment, and the parts inthis embodiment same as those in the first embodiment will be designatedby the same reference signs and descriptions thereof will be omitted.

FIG. 12 shows a τ−Q map serving as the fuel injection quantitycharacteristic storing means 54 in this embodiment.

In FIG. 12, the solid curve indicates the τ−Q characteristic at the railpressure Pcr (i.e. at the reference in-cylinder pressure Pcl′). When therequired fuel injection quantity is Q, the power supply time forattaining the required fuel injection quantity Q at the rail pressurePcr (at the reference in-cylinder pressure Pcl′) determined from the τ−Qcharacteristic indicated by the solid curve in FIG. 12 is τ1.

In FIG. 12, the broken curve indicates the τ−Q characteristic at thefirst virtual rail pressure (Pcr−ΔPcl) obtained by subtracting thedifference ΔPcl of the in-cylinder pressure of the engine Pcl and thereference in-cylinder pressure Pcl′ from the rail pressure Pcr under thecondition in which the in-cylinder pressure of the engine Pcl is appliedto the rail pressure Pcr. The power supply time for attaining therequired fuel injection quantity Q at the first virtual rail pressure(Pcr−ΔPcl) determined from the τ−Q characteristic indicated by thebroken curve in FIG. 12 is τ2.

As per the above, since in the stationary running state, the flow ratethrough the injection hole can be determined based on the pressuredifference between the interior and the exterior, injection with arequired fuel injection quantity can be attained by replacing the railpressure with the pressure difference between the rail pressure and thein-cylinder pressure of the engine as the virtual rail pressuredirectly. Therefore, in the stationary running state, additionalcalculation for correction is not required and errors throughcalculation hardly occur. The use of the pressure difference between therail pressure and the in-cylinder pressure of the engine as a virtualrail pressure corresponds to calculation of the first virtual fuelpressure by the first virtual fuel pressure calculation means 65.

However, the variation in the fuel injection start time is not correctedeven when the pressure difference is substituted for the rail pressure.This is because at the time of opening the needle valve 23, the area onwhich the in-cylinder pressure acts is small as compared to the area onwhich the fuel pressure acts, and because the deceasing speed of thefluid pressure in the control chamber 32 varies depending on the railpressure.

In view of this, in this embodiment, correction of the fuel injectionstart time is effected in the following manner.

FIG. 13 shows the relationship between the rail pressure Pcr and thefuel injection delay time Id in this embodiment. The map containing thisrelationship constitutes the fuel injection delay time calculation means67.

From the relationship shown in FIG. 13, the time difference Δτd betweenthe fuel injection delay time at the rail pressure Pcr and the fuelinjection delay time at a second virtual rail pressure (Pcr+ΔPcl)obtained by adding the difference ΔPcl of the in-cylinder pressure ofthe engine Pcl and the reference in-cylinder pressure Pcl′ to the railpressure Pcr is obtained.

A τ−Q characteristic in which the difference Aid between the fuelinjection delay time at the rail pressure Pcr and the fuel injectiondelay time at the second virtual rail pressure (Pcr+ΔPcl) has beencompensated is indicated as the dashed line in FIG. 12. In this case,the power supply time for attaining the required fuel injection quantityQ is τ3. The power supply time τ3 can be represented by the followingformula (15).τ3=τ2−Δτd  (15)

When the final power supply time thus determined is applied as the powersupply time for the fuel injection valve 8, the fuel injection can beeffected with improved accuracy in the injection quantity. Theabove-described process of obtaining the second virtual rail pressure(Pcr+ΔPcl) by adding the difference ΔPcl of the in-cylinder pressure ofthe engine Pcl and the reference in-cylinder pressure Pcl′ to the railpressure Pcr corresponds to calculation of the second virtual fuelpressure by the second virtual pressure calculation means 66.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to control the fuelinjection quantity that changes with changes in the in-cylinder pressurewith improved accuracy, and it is possible to attain a target fuelinjection quantity irrespectively of the running state of the internalcombustion engine.

1. A fuel injection control apparatus for an internal combustion engine equipped with a fuel injection valve for directly injecting high pressure fuel supplied by high pressure fuel supply means into a cylinder, comprising: in-cylinder pressure detection means for detecting or estimating in-cylinder pressure of said cylinder; time period calculation means for calculating fuel injection time period over which fuel is injected from said fuel injection valve, the fuel injection time period being corrected to compensate a variation in the fuel injection quantity caused by a variation in the fuel injection rate due to a variation in the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to a reference in-cylinder pressure that is stored in advance; start time variation calculation means for calculating a variation in the fuel injection start time at the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to the fuel injection start time at said reference in-cylinder pressure; control means for controlling the time period over which fuel is injected from said fuel injection valve based on the fuel injection time period calculated by said time period calculation means and the variation in the fuel injection start time calculated by said start time variation calculation means.
 2. A fuel injection control apparatus for an internal combustion engine according to claim 1, further comprising: fuel pressure detection means for detecting the pressure of the high pressure fuel supplied to said fuel injection valve by said high pressure fuel supply means; fuel injection quantity characteristic storing means for storing a characteristic, in relation to valve opening time of said fuel injection valve, of the fuel injection quantity injected by said fuel injection valve during the valve opening time in accordance with the pressure of the high pressure fuel supplied to said fuel injection valve by said high pressure fuel supply means; required fuel injection quantity calculation means for calculating a desired fuel injection quantity based on the running state of the internal combustion engine; fuel injection rate calculation means for calculating fuel injection rate based on the fuel pressure detected by said fuel pressure detection means and the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means; fuel injection quantity variation calculation means for calculating a variation in the fuel injection quantity caused by a variation in a second fuel injection rate calculated by said fuel injection rate calculation means based on the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to a first fuel injection rate calculated by said fuel injection rate calculation means based on said reference in-cylinder pressure; coefficient calculation means for calculating a variation in fuel injection delay time per unit in-cylinder pressure for the fuel pressure detected by said fuel pressure detection means, wherein, said time period calculation means calculates the fuel injection time period utilizing said fuel injection quantity characteristic storing means based on the variation in the fuel injection quantity calculated by said fuel injection quantity variation calculation means and the fuel injection quantity calculated by said required fuel injection quantity calculation means, said start time variation calculation means calculates the variation in the fuel injection start time based on a variation in the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to said reference in-cylinder pressure and the variation calculated by said coefficient calculation means.
 3. A fuel injection control apparatus for an internal combustion engine according to claim 2, further comprising: a needle valve provided in said fuel injection valve that moves in the axial direction to effect valve opening and closing operations; fuel injection quantity estimation means for estimating, when fuel injection by said fuel injection valve is started, the quantity of fuel injected since the valve opening operation of said needle valve is started until said needle valve reaches a full open state, based on the fuel pressure detected by said fuel pressure detection means and the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means; comparison means for comparing the estimated fuel quantity estimated by said fuel injection quantity estimation means and the fuel injection quantity calculated by said required fuel injection quantity calculation means, wherein, said fuel injection quantity variation calculation means calculates the variation in the fuel injection quantity using different calculation processes, in accordance with a result of the comparison by said comparison means, between in the case that said fuel injection quantity is less than said estimated fuel quantity and in the case that said fuel injection quantity is more than or equal to said estimated fuel quantity.
 4. A fuel injection control apparatus for an internal combustion engine according to claim 2, wherein said fuel injection quantity variation calculation means calculates the variation in the fuel injection quantity by modeling a change with time in the fuel injection rate as a polygon in a coordinate system and calculating a change in the area of said polygon.
 5. A fuel injection control apparatus for an internal combustion engine according to claim 3, wherein said fuel injection quantity variation calculation means further comprises: suction chamber pressure calculation means for calculating pressure in a suction chamber formed in the tip end side of a valve seat on/from which said needle valve is to be received/detached, based on the fuel pressure detected by said fuel pressure detection means and the position of said needle valve; unit fuel injection quantity variation calculation means for calculating a variation in the fuel injection quantity per unit in-cylinder pressure based on the fuel injection quantity calculated by said required fuel injection quantity calculation means and the suction chamber pressure calculated by said suction chamber pressure calculation means, wherein, when according to a result of the comparison by said comparison means, said fuel injection quantity is less than said estimated fuel injection quantity, said fuel injection quantity variation calculation means calculates the variation in the fuel injection quantity based on a variation in the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to said reference in-cylinder pressure and the variation in the fuel injection quantity per unit in-cylinder pressure calculated by said unit fuel injection quantity variation calculation means.
 6. A fuel injection control apparatus for an internal combustion engine according to claim 1, further comprising: fuel pressure detection means for detecting the pressure of the high pressure fuel supplied to said fuel injection valve by said high pressure fuel supply means; fuel injection quantity characteristic storing means for storing a characteristic, in relation to valve opening time of said fuel injection valve, of the fuel injection quantity injected by said fuel injection valve during the valve opening time in accordance with the pressure of the high pressure fuel supplied to said fuel injection valve by said high pressure fuel supply means; required fuel injection quantity calculation means for calculating a desired fuel injection quantity based on the running state of the internal combustion engine; first virtual fuel pressure calculation means for calculating a first virtual fuel pressure by subtracting a variation in the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to said reference in-cylinder pressure from the fuel pressure detected by said fuel pressure detection means; second virtual fuel pressure calculation means for calculating a second virtual fuel pressure by adding a variation in the in-cylinder pressure detected or estimated by said in-cylinder pressure detection means relative to said reference in-cylinder pressure to the fuel pressure detected by said fuel pressure detection means; injection delay time calculation means for calculating injection delay time from the time at which a signal for opening said fuel injection valve is generated to the time at which fuel injection by said fuel injection valve is started, based on the fuel pressure detected by said fuel pressure detection means, wherein, said time period calculation means calculates the fuel injection time period utilizing said fuel injection characteristic storing means based on the first virtual fuel pressure calculated by said first virtual fuel pressure calculation means and the fuel injection quantity calculated by said required fuel injection quantity calculation means, and said start time variation calculation means calculates, by means of said fuel injection delay time calculation means, a fuel injection delay time for the fuel pressure detected by said fuel pressure detection means and a fuel injection delay time for the second virtual fuel pressure calculated by said second virtual fuel pressure calculation means and calculates the variation in the fuel injection start time from a difference between those injection delay times.
 7. A fuel injection control apparatus for an internal combustion engine according to claim 3, wherein said fuel injection quantity variation calculation means calculates the variation in the fuel injection quantity by modeling a change with time in the fuel injection rate as a polygon in a coordinate system and calculating a change in the area of said polygon. 